Diabetes is a common disease that has a prevalence of 2-4% in the population. Non-insulin dependent diabetes mellitus comprises about 85% of diabetes most commonly occurring at the age above 40 years. The incidence of non-insulin dependent diabetes mellitus is increasing and is at a global level expected to surpass 200 million subjects at year 2010.
Diabetes is associated with increased morbidity and a 2-4-fold increase in mortality primarily due to cardiovascular diseases and strokes.
Non-insulin dependent diabetes mellitus develops especially in subjects with insulin resistance and a cluster of cardiovascular risk factors such as obesity, hypertension and dyslipidemia, a syndrome which first recently has been recognized and is named “The metabolic syndrome” (Alberti K. G., Zimmet P. Z.; Definition, diagnosis and classification of diabetes mellitus and its complications”. Part 1: Diagnosis and classification of diabetes mellitus provisional report of a WHO consultation. Diabet. Med. 1998 July; 15 (7), p. 539-53).
In accordance with the WHO-definition (www.idi.org.au/whoreport.htm), a patient has metabolic syndrome if insulin resistance and/or glucose intolerance is present together with two or more of the following conditions:    reduced glucose tolerance or diabetes    insulin sensitivity (under hyperinsulinaemic, euglycaemic conditions corresponding to a glucose uptake below the lower quartile for the background population)    increased blood pressure (≧140/90 mmHg)    increased plasma triglyceride (≧1.7 mmol/l) and/or low HDL cholesterol (<0.9 mmol/l for men; <1.0 mmol/l for women)    central adipositas (waist/hip ratio for men: >0.90 and for women>0.85) and/or Body Mass Index>30 kg/m2)    micro albuminuria (urine albumin excretion: ≧20 μg min−1 or albumin/creatinine ratio≧2.0 mg/mmol.
It has become increasingly evident that the treatment should aim at simultaneously normalizing blood glucose, blood pressure, lipids and body weight to reduce the morbidity and mortality. Diet treatment, exercise and avoiding smoking are the first treatment modalities that should be started. However, it will often be necessary to add pharmacological therapy but until today no single drug that simultaneously attacks hyperglycaemia, hypertension and dyslipidemia are available for patients with metabolic syndrome. Instead, these patients may be treated with a combination of several different drugs in addition to e.g., diet. This type or treatment is difficult to adjust and administer to the patient and such treatment may result in many unwanted adverse effects which in themselves may need medical treatment.
Consequently there is a long felt need for a new and combined medicament for the treatment of metabolic syndrome thereby also preventing an increase in the number of persons developing the non-insulin dependent diabetes mellitus.
Existing oral antidiabetic medicaments to be used in such treatment include the classic insulinotropic agents sulphonylureas (Lebovitz H. E. 1997. “The oral hypoglycemic agents”. In: Ellenberg and Rifkin's Diabetes Mellitus. D. J. Porte and R. S. Sherwin, Editors: Appleton and Lange, p. 761-788). They act primarily by stimulating the sulphonylurea-receptor on the insulin producing beta-cells via closure of the K+ATP-sensitive channels. However if such an action also affects the myocytes in the heart, an increased risk of cardiac arrhytmias might be present. Also, it is well know in the art that sulphonylureas can cause severe and lifethreatening hypoglycemia, due to their continuous action as long as they are present in the blood.
Consumption of soy protein rather than animal protein has been found to lower blood cholesterol (Anderson J. W., Johnstone B. M., Cook-Newell M. E.: Meta-analysis of the effects of soy protein intake on serum lipids. N. Engl. J. Med. 1995; 333; p. 276-282). In addition to this knowledge, recent research also provides evidence that soy protein and/or isoflavones may improve endothelial function and attenuate events leading to both lesion and thrombus formation (Anderson J. W., Johnstone B. M., Cook-Newell M. E.: “Meta-analysis of the effects of soy protein intake on serum lipids”; N. Engl. J. Med. 1995; 333; p. 276-282; Potter S. M., Soy protein and cardiovascular disease: “The impact of bioactive components in soy”. Nutrition Reviews 1998; 56, p. 231-235).
Several attempts to develop new antidiabetic agents and drugs for the treatment or prophylactic treatment of the syndrome not having the adverse effects mentioned above, e.g. hypoglycemia and potential harmful actions on the heart functions have been made over the years. For this purpose, plants provide a vast resource of compounds with the potential to become new antidiabetic agents.
For instance extracts of the leaves of Stevia rebaudiana Bertoni, a herbaceous member of the Compositae family, have been used for many years in the treatment of diabetes among Indians in Paraguay and Brazil (Sakaguschi M., Kan P Aspesquisas japonesas com Stevia rebaudiana (Bert) Bertoni e o estevioside. Cienc. Cultur. 34; p. 235-248, 1982; Oviedo C. A., Franciani G., Moreno R., et al. “Action hipoglucemiante de la Stevia Rebaudiana Bertoni (Kaa-he-e)”. Excerpt. Med. 209, p. 92, 1979; Curi R., Alvarez M., Bazotte R. B., et al. Effect of Stevia rebaudiana on glucose tolerance in normal adult humans. Braz. J. Med. Biol. Res., 19, p. 771-774, 1986; Hansson J. R., Oliveira B. H., “Stevioside and related sweet diterpenoid glycoside”. Nat. Prod. Rep. 21, p. 301-309, 1993).
Also, an antihyperglycemic effect has been found in rats when supplementing the diet with dried S. rebaudiana leaves (Oviedo C. A., Franciani G., Moreno R., et al. “Action hipoglucemiante de la Stevia Rebaudiana Bertoni (Kaa-he-e)”. Excerpt. Med. 209:92, 1979). Curi et al. found a slight suppression of plasma glucose when extracts of Stevia rebaudiana leaves were taken orally during a 3-day period. Furthermore, Oviedo et al. reported that tea prepared from the leaves caused a 35% reduction in blood glucose in man.
A number of Stevia species have been examined and shown to contain labdanes, clerodanes, kaurenes and beyerenes (Hansson J. R., Oliveira B. H., “Stevioside and related sweet diterpenoid glycoside”. Nat. Prod. Rep. 21, p. 301-309, 1993). Any of these substances as well as many others unidentified substances in the leaves could be responsible for the reduction in blood glucose in man.
In the work of Malaisse W. J. et al (Malaisse W. J., Vanonderbergen A., Louchami K, Jijakli H. and Malaisse-Lagae F., “Effects of Artificial Sweeteners on Insulin Release and Cationic Fluxes in Rat Pancreatic Islets”, Cell. Signal. Vol 10, No. 10, p. 727-733, 1998) the effect of several artificial sweeteners, including stevioside, on insulin release from isolated normal pancreatic rat islets were studied. In this study it was reported that in the presence of 7 mmol/l D-glucose, stevioside in a concentration of 1.0 mmol/l caused a significant increase in insulin output. Also the control group demonstrated a significant increase in insulin output of about 16 times above the basal release value in the presence of 20 mmol/l D-glucose increase. It is therefore uncertain whether the insulin releasing effect is due to the increased glucose level or the presence of stevioside. No diabetic islet cells were studied and the skilled person within the art will know that the mechanism for stimulating normal pancreatic islet cells either not functions at its optimum or not functions at all in the diabetic pancreatic cells, and that the study provided no certain indication of the possible use of stevioside in the treatment of non-insulin dependent diabetes mellitus, hypertension and/or the metabolic syndrome.
In a Chinese study (Lin Qi-Xian, Cao Hai-Xing, Xie Dong, Li Xing-Ming, Shang Ting-Lan, Chen Ya-Sen, Ju Rui-Fen, Dong Li-Li, Wang Ye-Wen, Quian Bao-Gong, “Experiment of Extraction of Stevioside”, Chinese Journal og Pharmaceuticals 1991, No. 22, p 389-390) is indicated a method for extracting stevioside from stevioside leafs from the origin of Bingzzhou in the Hunan Province. The content of stevioside in the extract was determined using HPLC although the article is silent of the purity of the extract. The produced stevioside tablets were for no apparent reason and medical indication applied to patients in the Wuhan Second Hospital. No data on the influence of stevioside on blood glucose, insulin and/or blood pressure is revealed. It is stated that the tablets were effective to diabetes and hypertension during preliminary clinical observations. However, total lack of data on blood glucose, insulin and/or blood pressure i.e., lack of support by test results and the missing information of which types of diabetes that were treated, makes this an unsupported and unconfirmed assertion.
Any detailed information of which substance or substances in the leaves that might cause a possible anti-hyperglycemic effect has not yet been disclosed for certainty, and the mechanism of how and to which extent the plasma glucose is reduced is unknown. The above mentioned articles and studies are concerned with the initial discovery of the effects and provide no evidence of which specific component(s) in the leaves that might be the active one(s).
The effect of intravenous stevioside on the blood pressure was studied in spontaneously hypertensive rats (“The Effect of Stevioside on Blood Pressure and Plasma Catecholamines in Spontaneously Hypertensive Rats”, Paul Chan, De-Yi Xu, Ju-Chi Liu, Yi-Jen Chen, Brian Tomlinson, Wen-Pin Huang, Juei-Tang Cheng, Life Science, Vol. 63, No. 19, 1998, p. 1679-1684). The study showed that during an intravenously administration of stevioside of 200 mg/kg the hypotensive effect was at a maximum, but although reported as being significantly the fall in the systolic blood pressure was only small. Neither the heart rate nor the plasma catecholamines were significantly changed during the observation period. This study indicated that stevioside advantageously could be used for treating hypertension.
No reports of an effect on plasma glucagon level have previously been reported. Glucagon, a pancreatic islet hormone, acts as a diabetogenic hormone by increasing the hepatic glucose output thereby elevating blood glucose.
Recent studies and tests made by the present inventors have focused on especially the diterpenoid glycoside stevioside which is a major constituent found in the leaves of Stevia rebaudiana where it may occur in amounts of up to about 10% (Hansson J. R., Oliveira B. H., “Stevioside and related sweet diterpenoid glycoside”. Nat. Prod. Rep. 21, p. 301-309, 1993; Bridel M., Lavielle R., Physiologie Vegetale: “Sur le principe sucre'du Kaa' he'e (Stevia rebaudiana Bertoni): II Les produits d'hydrolyse diastasique du stevioside, glucose et steviol”. Acad. Sci. Paris 192, p. 1123-1125, 1931; Soejarto D. D., Kinghorn A. D., Farnsworth N. R., Potential sweetening agent of plant origin. III: “Organoleptic evaluation of Stevia leaf herbarium samples for sweetness”. J. Nat. Prod. 45, p. 590-598, 1983; Mossettig E., Nes W. E. Stevioside. II: “The structure of the aglucone”; J. Org. Chem. 20, p. 884-899, 1955; Kohda H., Hasai R., Yamasaki K. et al. “New sweet diterpene glucosides from Stevia rebaudiana”. Phytochemistry 15, p. 981-983, 1976).
Also, its aglycone, steviol, has been found to be contained in the leaves of Stevia rebaudiana as well as other sweet-tasting glycosides e.g. Steviolbioside, Rebaudioside A,B,C,D and E, and Dulcoside (Bridel M., Lavielle R., Physiologie Vegetale: “Sur le principe sucre'du Kaa' he'e (Stevia rebaudiana Bertoni): II Les produits d'hydrolyse diastasique du stevioside, glucose et steviol”. Acad. Sci. Paris 192, p. 1123-1125, 1931; Soejarto D. D., Kinghorn A. D., Farnsworth N. R., Potential sweetening agent of plant origin. III: “Organoleptic evaluation of Stevia leaf herbarium samples for sweetness”. J. Nat. Prod. 45, p. 590-598, 1983; Mossettig E., Nes W. E. Stevioside. II: “The structure of the aglucone”; J. Org. Chem. 20, p. 884-899, 1955; Mossettig E., Nes W. E. Stevioside. II: “The structure of the aglucone”; J. Org. Chem. 20, p. 884-899, 1955; Kohda K., Hasai R., Yamasaki K. et al. “New sweet diterpene glucosides from Stevia rebaudiana”. Phytochemistry 15, p. 981-983, 1976).
The present inventors have already successfully proved that both stevioside and steviol have an anti-hyperglycemic, glucagonostatic and insulinotropic effect when administered intravenously to rats and a stimulatory effect on the insulin secretion from mouse islets in vitro.
No well defined, chemical stable, non-toxic, reliable and non-adverse effects alternative to the sulphonylureas for the treatment of non-insulin dependent diabetes mellitus is available today, however, and these findings have given rise to further studies and tests of analogues and derivates of these substances in order to find improved and alternative drugs for a self-regulatory treatment of diabetes, hypertension and especially metabolic syndrome in mammals, and preferably in humans.
In order to prevent sequelae or to delay the developing of a number of the above-mentioned metabolic and functional disorders in humans, there is a need it for new and beneficial dietary supplementations or new self-administrable non-prescription drugs for prophylaxis. The present invention now satisfies this need.